The present invention relates to an aggregate of pressure medium cylinders, especially for use where a relative large length of stroke is required. More specifically the invention comprises an aggregate of pressure medium cylinders where the piston rod of a first cylinder is directed away from the piston rod of a second cylinder where the cylinder portions of the cylinders are rigidly connected to each other and where the longitudinal axes of the cylinders run parallel to the longitudinal axis of the aggregate.
By the term xe2x80x9cmediumxe2x80x9d is meant preferably a gaseous or liquid fluid which is employed to drive the cylinders in the aggregate. On pressure setting each cylinder chamber with a gaseous or liquid fluid, the respective piston rod is pushed out, and reversely, on venting off the fluid from the cylinder chamber, the piston rod is drawn into the cylinder.
A usual problem with pressure medium cylinders, which have a relatively large length of stroke, is that they become unstable during use and are apt to break at the transition from cylinder to piston rod.
Attempts have been made to remedy this drawback by employing an aggregate of pressure medium cylinders in the form of a number of double acting telescopic cylinders, that is to say a number of cylinders which are arranged along a common central axis. However such an aggregate has a weakness having relatively thin piston rods in the final telescopic link and a corresponding danger of breaking at the transition from cylinder to piston rod in said final telescopic link.
In U.S. Pat. No. 4,733,598 a telescopic arrangement is referred to which comprises a simple aggregate of three telescopic pipes together with only two oppositely directed pressure medium cylinders. The cylinders are disposed side-by-side, that is to say roughly on each side of the central axis of the telescopic arrangement. The cylinders are secured to a telescopic pipe radially most central, while the respective piston rod has the outer end secured to a telescopic pipe radially outermost or radially innermost. The two cylinders are disposed side-by-side on each side of the central axis of the telescopic arrangement. The construction necessarily provides an oblique load between the outer ends of the piston rods in a direction which extends obliquely of the central axis of the aggregate/telescopic arrangement. The surrounding telescopic pipes are correspondingly obliquely loaded by the pressure medium cylinders, especially in the fully pushed out condition of the piston rods.
In U.S. Pat. No. 3,250,182 there is referred to according to FIGS. 1-7 a simple cylinder aggregate of a kind equivalent to that described in the afore-mentioned U.S. Pat. No. 4,733,598. In FIGS. 8-9 an arrangement is shown of a still simpler kind, without telescopic pipes and without a mechanical connection between the pressure medium cylinders, that is to say for completely different purposes than according to the invention.
With the present invention the aim is an aggregate having a robust and operatively reliable construction practically, where inter alia the danger of breakage of piston rods during use is reduced.
The aggregate according to the invention is characterised in that a number of cylinders of a first type and a number of cylinders of a second type are arranged in an annular group about the longitudinal axis of the aggregate, the cylinders of the first type being received in intermediate spaces between cylinders of the second type, while the piston rods of the first type of cylinders are rigidly connected to each other at associated outer ends, and the piston rods of the second type of cylinder are mutually rigidly connected to each other at associated outer ends.
By arranging pressure medium cylinders of a multi-cylindered cylinder aggregate according to the invention double stroke length and a multiple outgoing power can generally be achieved, that is to say double outgoing power in an aggregate of two cylinders and quadruple outgoing power in four cylinders, etc.
Consequently with a robust construction, but nevertheless a relatively short cylinder portion, there can be achieved a relatively large stroke length and simultaneously a relatively large outgoing power.
According to a first embodiment of the invention the aggregate is further characterised in that the cylinders of the first type are equipped with a first common power transmitting slide, and the cylinders of the second type are equipped with a second common power transmitting slide, the slides being arranged centrally between the cylinders and being slidable along a common central axis.
By means of the slides the accumulated outgoing power of the aggregate can be conveyed along the common central axis and relieve in an effective manner flexural stresses which otherwise would be able to occur in the piston rods.
According to a second embodiment of the invention the aggregate is further characterised in that the cylinder portions of the cylinders are made coherently of a common piece of material.
According to a third embodiment of the invention the aggregate is further characterised in that the piston rods of the first cylinders are at respective outer ends mutually rigidly connected to each other via their respective first local fastening points in a first plane, and that the piston rods of the second cylinders are at the outer end mutually rigidly connected to each other via their respective second local fastening point in a second plane which crosses the first plane.
By means of the annular arrangement of cylinders the total outgoing power can be readily localised along a common central axis, one being able to ensure with a mutually rigid connection between the piston rods at each of the ends of the aggregate that the total out going power of the aggregate can be conveyed along the common central axis. In addition flexural stresses, which could otherwise occur in the piston rods, can be relieved in an effective manner.
Consequently in the invention a larger number of pressure medium cylinders is employed than that which is known previously. With the new solution pressure medium cylinders which have the same piston outward displacement direction, can be placed in pairs, diametrically above each other on their respective sides of the central axis of the aggregate.
According to the invention the oblique loads which arise according to the US publications can be avoided. Consequently according to the invention the possibility is achieved for a more reliable mode of operation and the possibility for transmitting significantly greater pushing forces than those which are possible according to the US publications. According to the invention it is consequently a question of a new solution and a considerable advance in the field.